Frequency-scanned phased-array antennas are well known in the field and are usually operated at bandwidths that are at least a few percent. The traditional frequency-scanned phased array antenna using "hollow pipe" electromagnetic waveguide is described in detail in the book titled "Microwave Scanning Antennas", by R. C. Hansen, Vol.3, chapter two, Academic press, 1966. Although this technology has been very successful, it has limited present day applications because "hollow pipe" waveguide elements are too voluminous for the solid state, printed circuitry requirements now in widespread use for microwave and millimeter-wave radars. In addition, the bandwidths required (usually grater than six percent) are too large for practical solid-state millimeter-wave radars, which significantly limits the commercial applications of this technology.
FIG. 1 illustrates a more recent prior art frequency-scanned phased-array antenna 10 shown using electromagnetic transmission line 12 such as a microstrip. The operation of the frequency-scanned phased-array antenna 10 is described in greater detail in the article titled "Frequency Scanning Microstrip Antennas", by Magnus Danielsen and Roff Jorgensen, in IEEE Transactions on Antennas and Propagation, Vol. AP-27, No. 2, March 1979, pages 146-150, which article is incorporated herein by reference.
The Danielsen et al. article proposes a frequency-scanned phased-array antenna design where the transmission line 12 is formed of a plurality of segments, i.e., 14, 15, 16 that meander back and forth between successive patch radiating resonators, i.e., 18, 19, 20, 21. This meandering increases the electrical length of the transmission line segments between successive patch resonators. Therefore, the phase shift imparted by the transmission line 12 to a traveling wave is likewise substantially increased. In addition it should be noted that each patch resonator itself imparts a significant phase shift to the traveling wave.
However, the physical length and the electrical length of each microstrip transmission line segment 14, 15, 16 is limited by the geometry of the patch resonators 18, 19, 20, 21, so that the bandwidths required for a +45 degree to -45 degree-scan range still remain greater than six percent.